280 DR. H. LYSTER JAMESON ON 



wliilo in Part V. of the Report, p. 14, he and Hornell say : — 



" Some of onr Ceylon Pearl-Oyster parasites very closely 

 resemble the figures given by Giard " [i. e. of Seurat's larva] 

 " and possibly may also belong to the genus Cyathocephalus 

 [T't/locephalum], although most of them are certainly Tetra- 

 rhynchids " ; 



and on pp. 16-17 : 



" It is possible, however, that more than one species of 

 Cestode is represented — one is certainly a species of Tetra- 

 rhynchus {Rhynchohothrius)^ and another is probably the 

 same genus, or may possibly belong to Cyathocephalus . . . ." 



Later on, however (p. 20), Herdman and Hornell reject the 

 idea that the globular larvae may be Tylocephala or allied genera, 

 and, in discussing the opinions of Giard and Seurat on the 

 systematic position of Seurat's larva, they say that they regard 

 the terminal invagination, not as a sucker with a papilla on its 

 floor, but as 



" the opening in a hood or depression formed by the 

 sinking of the scolex into the front of its vesicle. The 

 changes of shape which we observed in this larva in' the living 

 state, the protrusion and retraction of the papilla-like part 

 which we regard as the anterior end of the scolex, agree with 

 this interpretation. Consequently, we are of opinion that this 

 larval Cestode is not one of the Monobothria — that it belongs 

 to neither the Pseud ophyllidea nor the Tetraphyllidea,, but is 

 a young Tetrarhynchid belonging to the Trypanorhyncha, and 

 we give here (fig. 4) a series of diagrams in order to show 

 the positions that we suppose our stages to occupy in the 

 development of such a form." 



Shipley and Hornell (Herdman's Report II. p. 80) call attention 

 to the resemblance of 'older examples of the larger la^YYa, {Tylo- 

 cephalum ltt,dijicans) to Seurat's form, and think there is little 

 doubt that they are at least generically the same (p. 82). Again, 

 Southwell says (39, p. 169) : 



" It would certainly appear more probable as well as 

 simpler, for this larva to develop into a Tylocephahmi (as is 

 believed by Seurat) than into a Tetrarhynchusr 



Again, Southwell, speaking of the great scarcity of the adult 

 of Tetrarhynchus tmionifactor in Elasmobranchs taken by trawling, 

 says (42 p. 130): 



" It would almost appear that this fact in itself is sufficient 

 proof that the adult of the pearl-inducing worm is not 

 Tetrarhynchus unionif actor. '" 



But at the foot of the same page he reverts to the position 

 that it is a Tetrarhynchus. 



